Process of removing backs from marine and fresh water shells



Patented Dec. 11, 1951 PROCESS OF REMOVING BACKS FROM MARINE AND FRESH WATER SHELLS Joseph H. Hooton, 'Englewood, N. J., assignor to Richelieu Corporation, New York, N. Y., a corporation. of New York No Drawing. Application March 24, 1949, Serial No. 83,289.

3 .Claims.

This invention relates to a novel process of removing backs from marine and fresh water shells.

Many marine and fresh water shells consist largely of a very attractive mother-of-pearl or nacre. This mother-of-pearl or nacre ismade up of laminations of fiat calcium carbonate particles (sometimes. called, crystals, scales, or platelets) held together by a proteinaceous substance known as conchiolin. Such shells are very attractive on the inside thereof but the outside surface is rough, scaly, porous, dull and very unattractive. Very attractive objects are sometimes made by grinding 01f the outside surface and polishing, the area underneath the surface; The grinding process, however, is a difficult and laborious process. If it is desired to obtain the lamillar crystals or nacreous material from the shells it is also desirable to remove the back portion to prevent contamination of the crystal products.

It has already been proposed to exfoliate the lamellae, or laminae of such shell by heat treating in an oven (see U. S. Patent No. 1,570,183), by heating with water under pressure (see U. S. Patent No. 1,812,885) or by treating with a mild alkaline solution with or without extraneous heating (see U. S. Patent 2,172,369). Such treatments appear to soften the proteinaceous binding material holding the laminae together so that the particles are easily separated. None of the above mentioned patents refer to any method of removing the backs from shells but it is presumed that either the backs are first removed by grinding or that the contaminating material of the back of the shell which cannot be removed by subsequent washing or decanting is permitted to remain in the product.

The normal method of removing the backs of such shells is by grinding with high speed abrading wheels. This process is expensive, laborious and creates a considerable amount of harmful and annoying dust.

An object of this invention is to provide a novel method of removing the backs of such marine or fresh water shells without exfoliating or otherwise disturbing the remainder or nacre-containing portion of the shell.

Another object of the invention is to provide a chemical method of removing the backs of marine and fresh water shells without exfoliating or otherwise destroying the nacre of the shell.

These results and others ancillary thereto are obtained by treating the shells at low. pressure and relatively low temperatures in an autoclave with an aqueous solution. The treatment is such that, if higher "temperature or a longer time of treatment were employed, exfoliation might result. It has been found, however, that the backs can be removed by a considerably milder type of treatment'than that required forexfol-iation. This may be due to the porous nature of the backs or it may be due tosomeother chemical or physical factor.

The exacttemperatureand pressure limits cannot be precisely defined since there is a wide range'of such limits. The pressure which is employed is the pressure which corresponds to the vapor pressure of the water vapor in the treating solution at the required temperature. As a practical matter temperatures of 102 C. to 198 C. (corresponding to steam gauge pressures of about 1 to 200 p. s. i.) ma be employed. The time element, however, is important in that the process is stopped before any exfoliation 0f the interior of the shell takes place. The lower the temperature and pressure the longer it is necessary to treat the shells. Under the treatment as usually conducted, cracks appear in the back of the shells and the large fragments defined by the cracks separate at the edges from the rest of the shell and can be easily removed by hand or by passing under a brushing mechanism.

The aqueous solution which is employed can be ordinary tap water if the temperature is raised sufiiciently but preferably the water is made slightly alkaline. The best alkaline agent for effecting the separation of the back, at such a rate that there is no exfoliation of the remainder of the shell, are the alkali phosphates such as trisodium phosphate, disodium phosphate and mixtures thereof.

The novel features characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying examples in which:

Example 1 A solution of seven pounds of trisodium phos-v raised to about 174 C. (corresponding to about 111 p. s. i. steam gauge pressure). The process is continued for about two hours when the steam pressure is turned off and the shells are permitted to remain in the autoclave until cooled.

When the shells are removed from the autoclave it is found that the back breaks ofi in large fragments when subjected to shearing stress.

Example 2 A quantity of shells having the scientific name of Placuna Sella Gmelin is placed in an autoclave so as to substantially half fill the same. Sufiicient trisodium phosphate solution containing about a pound of commercial trisodium phosphate per gallon of Water is added to completely submerge the shells. The autoclave is then closed and the shells are treated at about 178 C. (corresponding to about 125 p. s. i. of steam gauge pressure) for 100 minutes.

The loosened backs can be easily removed by brushing with a wire brush.

I claim:

l. A process of removing backs from marine and fresh water shells comprising the steps of placing the shells in an autoclave, covering said shells with an aqueous solution of an alkali phosphate selected from the group consisting of the trialkali phosphates and the dialkali phosphates and mixtures thereof, closing the autoclave, subjecting the shells to heat treatment corresponding to steam gauge pressure of 1 to 200 p. s. i. for a sufficient time to cause the backs of the shells to crack and separate from the remainder of the shell, and then stopping the treatment before any exfoliation of the bod of the shells takes place.

2. A process of removing backs from marine and fresh water shells comprising the steps of subjecting the shells to heat treatment corresponding to steam gauge pressure of 1 to 200 p. s." i. in the presence of an aqueous solution of trisodium phosphate, for a suflicient time to cause the backs of the shells to crack and separate from the remainder of the shell, and then stopping the treatment before any exfoliation of the body of the shells takes place.

3. A process of removing backs from marine and fresh water shells comprising the steps of subjecting the shells to heat treatment corresponding to steam gauge pressure of 1 to 200 p. s. i. in the presence of an aqueous solution of trisodium phosphate for a sufiicient time to cause the backs of the shells to crack and separate from the remainder of the shell, stopping the treatment before any exfoliation of the body of the shells takes place, removing the shells from the autoclave and separating the shell backs from the bodyof the shell by applying shearing stress to the backs of the shells.

JOSEPH H. HOOTON. 1

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,570,183 Rouschenberg Jan. 19, 1926 1,812,885 Lippincott July 7, 1931 1,823,136 Frederick Sept. 15, 1931 2,306,292 Atwood Dec. 22, 1942 2,380,741 Fischer July 31, 1945 

1. A PROCESS OF REMOVING BACKS FROM MARINE AND FRESH WATER SHELLS COMPRISING THE STEPS OF PLACING THE SHELLS IN AN AUTOCLAVE, COVERING SAID SHELLS WITH AN AQUEOUS SOLUTION OF AN ALKALI PHOSPHATE SELECTED FROM THE GROUP CONSISTING OF THE TRIALKALI PHOSPHATES AND THE DIALKALI PHOSPHATES AND MIXTURES THEREOF, CLOSING THE AUTOCLAVE, SUBJECTING THE SHELLS TO HEAT TEMPERATURE CORRESPONDING TO STEAM GAUGE PRESSURE OF 1 TO 200 P.S.I. FOR A SUFFICIENT TIME TO CAUSE THE BACKS OF THE SHELLS TO CRACK AND SEPARATE FROM THE REMAINDER OF THE SHELL, AND THEN STOPPING THE TREATMENT BEFORE ANY EXFOLIATION OF THE BODY OF THE SHELLS TAKES PLACE. 